Heat transfer fin heat exchanging tube



Jan- 3, 1967 YOSHIZO OKAMOTO ETAL 3,295,599

HEAT TRANSFER FIN HEAT EXCHANGING TUBE Filed April 5, 1963 Fig.

ATTORNEY.

United States Patent 3,295,599 HEAT TRANSFER FIN HEAT EXCHANGING TUBEYoshizo Okamoto, Tokai-mura, Naka-gun, Ibaragl-ken, Shinichi Negoya,Hitachi-shi, Ibaragi-ken, and Ken Namatame and Miyoshi Ohuchi,Tokai-mura, Nak agun, Ibaragi-ken, Japan, assignors to Nil onGenshiryoku Kenkyujo, Tokyo, Japan, a corporation of Japan Filed Apr. 5,1963, Ser. No. 270,860 Claims priority, application Japan, Apr. 23,1962, 37/ 15,650 1 Claim. (Cl. 165-484) The present invention relates,to improvements in the heat dissipating fins of heat exchanging tubes,as for in stance, a fin in a cladding tube enclosing a fuel element of anuclear reactor, where a number of longitudinal fins are usuallyprovided.

Generally, longitudinal fins providing heat transfer surfaces are, ascompared with other kinds of fins, more advantageous that any otherkinds of fins by reason of the fact that they can furnish a high heattransfer rate without increasing pressure loss and that they have a muchgreater operative heat transfer area in the cooling passage. As aconsequence, the pressure loss thereby incurred is five or six times aslarge as that of the heat transfer surface of a cylindrical tube,whereas heat transfer rate may be increased up to ten to fifteen timesthat in the same tube. However, longitudinal fins have otherdisadvantages. If the number of fins is increased in order to obtain ahigh efiiciency of heat transmission, it follows that the space betweenadjacent fins will become narrow and therefore the flow is turbulentbetween the closely spaced fins. This will cause lowering of flowvelocity to one third of the outside flow, and the effective heattransfer coefficient will be reduced accordingly as, for instance, whenthe number of fins is of the order of several scores, the heat transferarea becomes thirty times as large as the original tube, but theeffective heat transfer rate will remain at an approximate value ofseven to ten times as large. Also, under high temperature,non-uniformity of temperature on the surface of fins often gives rise tobe repeated stress, thermal deformation, bending, and excessive localheating of fins, which may limit the possibility of good design for theheat transfer surface of a fin.

The present invention is such that a number of helical grooves aredefined between the adjacent ends of axially aligned radially extendingfin elements formed on the external surface of a cylindrical tube, thusto improve the heat transfer characteristics of fins by diagonallyextending turned-over projections formed during the cutting of thediagonal or helical grooves in the longitudinal fins to form the finelements.

The present invention will be described, by way of example, withreference to the accompanying drawing, in which:

FIGURE 1 is a perspective view of a part of a cooling tube having heattransmission fins.

FIGURE 2 is a transverse section of FIGURE 1.

FIGURE 3 is an enlarged fragmentary front view show- 3,295,599 PatentedJan. 3, 1967 ing the arrangement of fin elements on the tube of presentinvention.

FIGURE 4 represents a fragmentary perspective view showing a single finelement.

FIGURE 5 is a perspective view of a modified heat exchanger havinghelical guide strips extending radially outwardly of the fin elements.

FIGURE 6 is a transverse section of FIG. 5.

The embodiment shown in the drawing is explained in more detail. InFIGURES l and 2, 1 is a tube having a heating source inside as, forinstance, a nuclear fuel element (not shown). On the outer surface ofthe tube, there are provided integrally formed fin elements 2 alignedaxially of the tube. However, between the confronting ends of adjacentfin elements 2, there are a series of diagonally cut grooves 3 definingparallel interrupted helical slots 4 extending circumferentially aroundthe tube 1. This is best shown in FIGURE 3, where a number ofinterrupted helical slots, extending as indicated by the arrow A, aredefined by the. grooves 3. Due to a turning over of the metal during thecutting of the diagonal grooves 3, there are produced convergentlaterally projecting edges 2a, 2b on both ends of each fin element 2.(Refer to FIGURE 4.) Coolant gas therefore flows between laterallyadjacent longitudinal rows of fin elements 2 and then runs through thediagonal grooves 3, being deflected by the convergent projecting edgeportions 2b, 2a of each lower and upper end. For example, the coolantgas flows along dotted lines in FIGURE 3. Therefore, each fin element 2will have much larger effective heattransfer area than that ofconventional continuous longitudinal fins.

FIGURES 5 and 6 show a modified embodiment where the fin elements 2 arecombined with several helical guide members 4 for guiding the coolantgas. The guide memhere are positioned in the helical slots defined bydiagonal grooves 3 between longitudinally adjacent fin elements 2, thecooling effect of each fin element 2 between guide members 4 being thesame as FIGS. 1 to 4.

While we have shown and described what we believe to be the bestembodiments of our invention, it will be apparent to those skilled inthe art that various changes and modifications may be made thereinwithout departing from the spirit and scope of the invention as definedin the appended claim. 4

What we claim is:

A heat exchanger comprising: an elongated tube; a series of spaced finelements formed on the external surface of said tube, each of said finelements extending radially outwardly from said external surface and'being elongated axially of said tube, said fin elements being alignedin regularly circumferentially spaced axially ex tending rows, the endsof adjacent fin elements in each row being spaced to define a groovetherebetween the bottom of which extends along said external surfacediagonally with reference to the axis of said tube, said grooves in eachrow being staggered with respect to the grooves in both adjacent rows todefine regularly axially spaced series of interrupted helical slotsextending circumferentially completely around said tube, each of saidfin elements having a convergent laterally projecting edge portionformed at each end thereof, said edge portions projecting in onedirection at one end of every fin element and on the opposite directionat the opposite end of every fin element, said edge portions extendingin opposite directions at opposite sides of each helical slot, wherebycooling fluid flowing longitudinally of said tube in either direction isdeflected laterally through said helical slots.

References Cited by the Examiner UNITED STATES PATENTS 10/1952 Newlin165184 1/ 1954 Chapman 165-184 9/1954 Legatski 165181 X 3/1961 Latharn165--184 X 5/1961 Fairhurst 165183 8/1963 Nihlen et a1 29157.3

FOREIGN PATENTS 8/ 1955 Belgium. 9/ 1959 Great Britain.

FREDERICK L. MA'ITESON, I R., Primary Examiner.

CHARLES SUKALO, Examiner.

